This invention relates to combustion systems and more particularly to an apparatus for venting the gaseous products of combustion from a combustion system. Specifically, this invention relates to a spillage damper for use in venting the gaseous products of combustion from an induced draft combustion system, such as a furnace.
A combustion system or furnace normally contains a combustion chamber wherein fuel, such as natural gas or oil, is burned creating hot gaseous products of combustion, a heat exchanger wherein the heat from the products of combustion are transferred to another medium such as air or water, and a flue or venting system wherein the gases, now referred to as flue gases, pass from the heat exchanger to atmosphere at a remote location. In a natural draft combustion system the flue gases usually are collected at a draft hood after the gases have passed over a heat exchanger. The draft hood is connected to a flue pipe whereby the flue gases are drawn into the flue pipe from the draft hood due to the natural draft of the flue pipe. In a forced draft combustion system a fan is located upstream of the combustion chamber and the heat exchanger and forces air into the combustion chamber and the products of combustion through the heat exchanger into the flue. In an induced draft combustion system a fan is located between the heat exchanger and the flue and draws air into the combustion chamber and draws the products of combustion through the heat exchanger into the flue. The forced draft and induced draft combustion systems are generally referred to as power draft combustion systems.
In the natural draft system the flue or vent system usually contains a means, such as a draft hood or draft diverter, for preventing pressure buildup in the flue system if the system is blocked. Draft hoods consist of an opening in the flue system covered by a hood. The opening allows the flue gases to vent to the atmosphere surrounding the furnace when pressure above atmospheric pressure builds up in the flue. When the flue is functioning normally the reduced pressure in the flue draws air through the opening into the draft hood and up the flue.
In addition to providing relief for pressure in the flue, the draft hood provides dilution of the products of combustion in the natural draft system. That is, the temperature and humidity of the products of combustion are reduced by mixing with air taken in through the draft hood opening. The air drawn into the flue through the draft hood opening is air which surrounds the furnace and is air which, in most instances, has been heated to room temperature. This, in effect, is a heat loss. That is, energy in the form of gas or oil has been used to heat the air which is subsequently drawn into the flue and expelled to the atmosphere. Reduction or elimination of this induced air reduces the heat loss and improves the system efficiency.
The draft hood or draft diverter of the natural draft combustion system may be used with a forced or induced draft combustion system. However, it is desirable to have an apparatus which provides the advantages of a draft hood or draft diverter such as relieving pressure in the vent system if the system should become blocked while eliminating or substantially reducing the heat loss associated with the draft hood or draft diverter and providing greater efficiency.